Field of the Invention
The present invention relates to a wire electric discharge machine with an automatic wire connecting function, capable of repairing breakage in the vicinity of a breakage position.
Description of the Related Art
In a wire electric discharge machine, a wire electrode may sometimes be broken while a workpiece is being machined. An automatic wire connecting function to reconnect the broken wire electrode is a known technique to solve this problem (e.g., Japanese Patent Applications Laid-Open Nos. 5-212623 and 5-337743).
In taper machining based on wire electric discharge machining such that a workpiece is inclined at a certain angle as it is machined by a wire electrode, unexpected breakage of the wire electrode may intermittently occur depending on difficulties in the machining shape, machining conditions, physical properties of the material of the workpiece, etc.
To overcome this, a wire electric discharge machine has an automatic wire connecting function such that a storage device attached to its controller is stored with a program for breakage repair in the vicinity of a breakage position. Based on the automatic wire connecting function, breakage repair processes are performed according to the preset program. The processes include breakage during machining, wire electrode rewinding, wire electrode tip cutting, wire connecting operation in the vicinity of the breakage position, completion of the wire connection, and restart of the machining, which occur or are carried out in the order named. In this way, the breakage repair can be performed in the vicinity of the breakage position without returning to a machining start point.
Even by the use of the conventional wire electric discharge machine, breakage of the wire electrode that occurs during taper machining can be repaired in the vicinity of the breakage position by the automatic wire connecting function. According to the prior art technique, however, the connection success rate of the breakage repair in the vicinity of the breakage position during the taper machining is drastically degraded as a taper angle and the distance between the respective Z-axis positions (heights) of the top surface of a workpiece and an upper die guide fulcrum increase. Therefore, the taper angle that ensures satisfactory wire connection in the vicinity of the breakage position during the taper machining by means of the automatic wire connecting function is limited to a small value.